1. Field of the Invention
This invention concerns a manufacturing method of a semiconductor device. In particular, the invention relates to analyzing optical constants of a measurement pattern on the semiconductor device thereby feeding back film thickness and composition data for adjusting the relevant manufacturing process.
2. Description of Related Art
As a method for measuring the composition and the thickness of a thin film used in a semiconductor, ellipsometry, has been generally adopted. FIG. 11 shows an example of an ellipsometric device, a spectro-ellipsometer, which measures light-polarization rotation.
An incident light emitted from a light source 20 is passed through a modulator 21 and separated by a polarizer 22 into a P-polarized component and an S-polarized component. The incident light is reflected by an object of interest 23, passed through a detector 24 and then polarized by a polarizer 25 into lights at wavelength from 250 nm to 830 nm. The spectralized light at each wavelength is adapted to be detected by a detector 26.
This method is adapted to enter a P-polarized light and an S-polarized light into a sample and determine the film thickness or the like based on the amplitude and the phase difference of the reflected lights, which is used generally as a method for measuring a thin film grown on the entire surface of a semiconductor wafer. In this case, the ellipsometric angle (xcfx86, xcex94) is defined through a complex reflection coefficient ratio p (ratio of the reflection coefficient rp of the P-polarized light, and the reflection coefficient rs of the S-polarized light) by the following equation:
xcfx81=rp/rs=tanxcfx86xc2x7exp(jxcex94) 
tanxcfx86=|rp|/|rs|
xcex94=xcex4RPxe2x88x92xcex4RS 
That is, tanxcfx86 represents a difference of amplitude, and xcex94 represents a constant indicating a phase difference between P-polarized light and S-polarized light. The film thickness, the composition or the like of the sample of interest can be determined by determining xcfx86 and xcex94 of the sample by comparing them with those of a known substance.
Usually, the spot size of incident light is several mm, which can be restricted to several tens xcexcm. However, the restriction of the incident light involves a problem that the signal intensity is decreased and the measuring accuracy is reduced. The incident angle and the reflection angle are usually about from 50xc2x0 to 75xc2x0. This technique is described in xe2x80x9cELLIPSOMETRY AND POLARIZED LIGHTxe2x80x9d, R. M. A, AZZAM AND N. M. BASHARA, NORTH-HOLLAND PUBLISHING COMPANY, 1977, pp 364-416.
Another method for measuring the thin film used on a semiconductor wafer is a reflectance method, and FIG. 12 shows the device and the principle thereof. In this technique, a white light at a wavelength, for example, of 200 nm to 900 nm is emitted from a light source 20 and entered at an angle nearly vertical to the sample 23, and the reflectance R of the light is measured by a detector 26. The reflectance R is generally represented by the following equation:
R=((nxe2x88x921)2+k2)/((n+1)2+k2) 
where n represents a refractive index and k represents an extinction coefficient.
This is a method for determining the film thickness and the composition of a substance based upon the principle that the wavelength dependence of n and K is a function of an energy gap of the substance. Since a perpendicular incident light is used in this method, the spot area on the sample is smaller compared with that in the ellipsometry, but it also has another problem that the restriction of the incident light decreases the signal intensity and the measuring accuracy. Further, it is difficult to apply an incident light to a fine pattern of 1 xcexcm or less. This technique is described in xe2x80x9cOPTICAL PROPERTIES OF CRYSTALLINE SEMICONDUCTORS AND DIELECTRICSxe2x80x9d A. R. FOROUHI AND I. BLOOMER, PHYSICAL REVIEW B. 38, P. 1865, (1988).
The base area of an SiGe hetero bipolar transistor is formed by SiGe epitaxial growth in which a selective growth method of depositing only on a fine transistor pattern is used. A cross sectional view of a hetero bipolar transistor using selective growth is shown in FIG. 13.
After forming a stacked film comprising a first silicon oxide film 30, a silicon nitride film 31, a polysilicon layer 32 for extrinsic base, and a second silicon oxide film 33, a predetermined transistor pattern is etched to expose the surface of a silicon substrate 3. Then, an SiGe selectively grown layer 34 as the base area of the transistor is formed only to the area where silicon is exposed. In the selective growth described above, since a so-called loading effect is often caused that a grown film thickness differs depending on the size of the grown area, the thickness of the actual film grown on the transistor area is different from that grown on a large area.
FIG. 14 shows an example of a loading effect, from which it can be seen that the selective growth thickness differs greatly depending on the area of the window in the dielectric film. Further, even the growth rate is decreased by lowering the growth pressure from 10000 Pa to 1000 Pa, the loading effect can not be eliminated completely. Accordingly, the thickness of the film grown on the actual transistor area can not be known unless the thickness of the film grown on the pattern of the same area as that for the transistor area is measured.
The transistor area often forms in a rectangular shape, for example, of about 0.2 xcexcmxc3x974 xcexcm, but it is difficult to transmit a light beam only to such a fine pattern by the ellipsometry described above. Accordingly, the film thickness of the selectively grown layer is confirmed by observing the cross section of a transistor main body under destructive inspection, such as by using a scanning type electron microscope.
The measurement of the film thickness on the fine pattern by the ellipsometry is extremely difficult since the signal intensity is low and tends to be interfered by the circumstantial structure. Further, the method for measuring the fine cross section of a transistor with a microscope requires much labor and is not usable in the product line since this applies destructive detection. That is, the thin film has been measured by using a sample wafer instead of the manufactured device wafer itself
As described above, it has been difficult to measure the composition and the thickness of a fine selectively grown semiconductor thin film by a non-destructive test. However, in the mass producing LSIs, it is necessary to control the process quality with a non-destructive inspection method. That is, it has been required for a method for determining a thickness of a selectively grown layer with respect to a wafer main body used for manufacturing the device, instantly feeding back a failure, if occurs, to a next batch so as to re-design the growth conditions.
This invention has been accomplished in view of the foregoing and it intends to provide a non-destructive inspection method for a selectively grown film and provide a manufacturing method of a semiconductor device for attaining a simple and convenient process control and improvement of the throughput.
In accordance with this invention, for attaining the foregoing object, an area larger than the spot size of an incident light of an ellipsometer (ellipsometric device) in which fine transistors are present densely is provided on a wafer for preparing LSI, and the optical constants of the entire area are determined by ellipsometry. By the analysis of the result, the thickness of an SiGe film, for example, grown selectively on the fine transistor pattern is determined. The growing conditions for the next batch of the thin film are determined based on the result of the measurement. Such a technique is effective in a so-called batchwise processing device in which wafers are treated sheet by sheet.
As described above, this invention has a feature in determining the thickness and/or the composition of a thin film grown in at least one trench on a semiconductor wafer on which surface plural substances are exposed by using a measurement pattern formed on the semiconductor wafer thereby determining growth conditions for a next batch of the thin film based on the comparing result.
This invention also has a feature in the constitution described above in that the measurement pattern has a larger area than the spot size of an incident light of the ellipsometer, while optical constants over the entire area are determined byellipsometry. The thickness of the thin film is measured based on the thus determined result, and the growth conditions for a next batch of the thin film are decided based on the measuring result.
This invention further has a feature of using a measurement pattern disposed on a wafer for manufacturing a semiconductor device having a thin film formed on a semiconductor substrates in which plural substances are exposed on the surface thereof and in which an area ratio between an area containing plural substances exposed on the wafer surface and other area is already known, then measuring optical constants of the entire measurement pattern before and after the growth of the thin film by ellipsometry, and determining the thickness and the composition of the thin film grown on each of the plural substances based on the measuring result.
This invention has a further feature in the constitution as described above in that the differential spectrums of optical constants before and after the growth of the thin film are analyzed based on the area ratio of the plural substances being exposed on the wafer surface before the formation of the thin film and the thickness and the composition of the thin film are determined based on the analyzing result.
This invention has a further feature in the constitution described above in that the measurement pattern comprises a semiconductor integrated circuit itself and is disposed by at least one semiconductor integrated circuit pattern.
This invention further has a feature in comprising a step for forming a dielectric film on the surface of a semiconductor substrate, a step for forming a window in the dielectric film through which a portion of the surface of the semiconductor substrate is exposed, a step for growing a semiconductor in the window, and the steps of determining the dielectric film thickness using the semiconductor as a measurement pattern and deciding growth conditions of the film thickness for next batch based on the determining result.
Other and further objects, features and advantages of the invention will appear more fully from the following description.